A magnetic disk drive has a rotating magnetic disk, and a magnetic head slider holding a read/write device, supported by a magnetic head support mechanism provided with a suspension and capable of being positioned with respect to a direction parallel to a diameter of the magnetic disk. The magnetic head slider runs over the magnetic disk relative to the magnetic disk, to read magnetic information recorded on the magnetic disk, and to write magnetic information to the magnetic disk. The magnetic disk slider is caused to float by the wedge effect of an air film serving as an air bearing so that the magnetic head slider may not come into solid contact with the magnetic disk.
A magnetic recording pattern needs to be miniaturized and the coercive force of the recording film of a magnetic recording medium needs to be enhanced to increase the recording density of magnetic recording. Japanese Patent Publication No. 2006-185548 discloses a recording magnetic field having a magnitude of intensity about twice the coercive force of a recording film needs to be created by a magnetic recording head to record magnetic information on a magnetic recording medium. The size of the tip of the magnetic pole of a magnetic device is progressively reduced with the progressive miniaturization of the magnetic recording pattern, and hence the intensity of a magnetic field created by the recording device is limited. Consequently, difficulty in applying a recording magnetic field having a magnitude of intensity about twice the coercive force of the recording film to the recording medium to achieve a still higher recording density becomes a problem.
To solve this problem, there has been proposed a heat-assisted recording method that reduces the coercive force of the recording film by heating a recording film when a write element applies a recording magnetic field to a recording medium to enable a magnetic field that cannot record magnetic information unless the recording film is heated to record magnetic information. Japanese Patent No. 3471285 discloses a heat-assisted recording method that uses a heat source included in a slider. Japanese Patent No. 3441417 discloses a heat-assisted recording method that uses an optical wave guide for a laser beam included in a slider and heats a recording film by near-field light emitted by a near-field light emitting device disposed near a write element when a laser beam passes the near-field light emitting device.
When a magnetic head is provided with a built-in heating mechanism for heat-assisted recording as mentioned above, heat generated by the heating mechanism heats a space around a read/write device included in a magnetic head. Consequently, the size of a thermal protrusion on the order of nanometers occurs due to thermal expansion.
Reduction of the distance between the slider and the magnetic disk of a magnetic disk drive, namely, the floating height of the slider, to increase linear recording density is effective in increasing the recording disk of the magnetic disk drive. Recently, the floating height of the slider has been reduced to 10 nm or below. In designing the floating height of the slider, the reduction of floating height attributable to machining errors, difference in the atmospheric pressure of a working environment and difference in the temperature of a using environment are estimated and a floating height margin is estimated so that the slider may not come into contact with the disk even under the worst condition.
There are two modes of floating height reduction depending on the difference in temperature of the working environment. A first mode of floating height reduction is thermal protrusion of a size on the order of nanometers caused by thermal expansion resulting from heating the vicinities of the read/write device of the head by heat generated by eddy-current loss (iron loss) in the magnetic pole caused by electromagnetic induction that occurs when a recording current flows through the coil and heat generated by the coil when a recording current flows through the coil (ohmic loss). A second mode of floating height reduction is local thermal protrusion of a size on the order of nanometers caused by the rise of environmental temperature resulting from difference in coefficient of linear thermal expansion among the magnetic shield around the read/write device, the metallic material and resins of the magnetic pole, and ceramic materials of other parts.
The size of a thermal protrusion caused by the heating mechanism for heat-assisted recording is added to a size of the thermal protrusions caused by heat generation by recording and the size of a thermal protrusion caused by difference in environmental temperature. Such a thermal protrusion of the added size has a significant effect on the floating height of 10 nm or below and is possible to cause contact between a magnetic head and a magnetic disk.